Service line protection valve



INVENTOR Ellery R. I'p'fiC/v BY g .E 74 Q g ATTORNEYS E. R. FITCH SERVICE LINE PROTECTION VALVE Filed. 001;. 31, 1949 Nd NQ March 17, 1953 Patented Mar. 17, 1953 UNITED STATES OFFICE SERVICE LINE PROTECTION VALVE Application October 31, 1949, Serial No. 124,631

15 Claims.

This invention relates to fluid pressure braking systems for tractor-trailer vehicles and more particularly to a valve construction for conserving fluid pressure on the tractor for efficient braking operations, notwithstanding the occurrence of a break or leak in certain of the brake lines on the vehicle.

In fluid pressure braking systems of the type generally utilized for tractor-trailer vehicles, the same have been so arranged as to provide interconnected service and emergency lines on the vehicles, the service lines being provided for the usual service applications of the brakes, while the emergency lines are employed for automatically applying the trailer brakes in the event of rupture or severe leakage of the emergency lines. During the usual service brake applications, fluid pressure is conducted from a source on the tractor to the tractor brake chambers and such pressure is also fed to the trailer service .line to operate a relay valve and thereby connect a trailer reservoir to the trailer brake chambers. Should the tractor or trailer service lines become broken or develop a severe leakage, fluid may be released from the source so rapidly that an effective service brake application on the tractor could not be obtained. Moreover, under such conditions, the leakage of fluid may be such as to prevent the trailer relay valve from operation and thus a total failure of both the tractor and trailer brakes would result.

Accordingly, the principal object of the present invention is to provide a fluid pressure braking system for tractor-trailer vehicles which is so constituted as to avoid the objections and disadvantages referred to above.

Another object is to provide in a fluidbraking system for tractor-trailer vehicles, a novel arrangement for conserving the fluid pressure on the tractor in the event of a severe leak or breakage of the service lines of the tractor or trailer.

A further object is to provide a novel control device on the tractor which is adapted to be interposed in the tractor service line and is operative to interrupt the flow of fluid therethrough after a predetermined time interval, in the event that the fluid flow through the service line exceeds a predetermined rate.

Still another object resides in the provision of a cut-oil valve arranged in the tractor service line, together with a novel control therefor, such control being responsive to a pressure differential measured between two points in the tractor service line and functioning with a time delay 2 action to energize the cut-01f valve and thereby prevent flow of fluid through said tractor service line.

A still further object is to provide a novel, relatively simple but highly effective and reliable control device for enabling application of the tractor brakes while preventing loss of fluid through a broken service line.

Still another object comprehends the provision of a control device of the above character, which is positive in its operation and which does not interfere with the normal operation of the brake systems on the two vehicles.

Other objects and novel features of the invention will appear more fully hereinafter from the following detailed description when taken in connection with the accompanying drawing illustrative of one form of the invention. It is to be expressly understood however that the drawing is employed for purposes of illustration only and is not to be taken as a definition of the limits of the invention, reference being had for this purpose to the appended claims.

Referring to the drawing, the single figure diagrammatically illustrates the present invention in connection with a tractor-trailer braking system, certain of the parts being shown in section.

More particularly, and as shown, the present invention is employed in connection with a tractor-trailer braking system of a well-known type adapted to be operated by air under pressure. For example, the tractor braking system includes a compressor [0 for supplying compressed air through a conduit l2 to a pair of serially connected reservoirs l4 and 16, the loading and unloading of the compressor being preferably controlled by a governor 58, connected to the compressor it as by means of a conduit 20. Governor l8 may be of any suitable construction such as that disclosed in the patent to B. S. Aikman No. 1,754,218, granted April 15, 1930. Front and rear braking chambers 22 and 24 are provided for respectively applying the front and rear brakes of the tractor and these chambers may be supplied with air pressure from the reservoir [5 through conduits 26, 27, 23, 3t, 32, 34, 36 and 38, a suitable pedal operated brake valve 40, which may be constructed as shown in the patent to W. J. Andres et al. No. 2,133,275, granted October 18, 1938, being associated with the conduits 28, 21 and 34 in order to control the degree of brake application of the front and rear brake chambers.

In order to provide suitable connections for the trailer braking system, the tractor braking system includes an emergency line 42 comprising conduits 44 and 45, as well as a service line 48 which includes conduits 50 and 52. The emergency and service lines 42 and 48 terminate in coupling parts of well-known construction which are adapted to be coupled with similar parts associated with the trailer braking system in order to provide releasable couplings 54 and 55. In addition, the trailer emergency and service lines 42 and 48 are respectively provided with cut-off cocks 58 and 60 in order to positively cut off these lines when the couplings 54 and 56 are disconnected prior to separation of the vehicles.

The trailer braldng system includes a plurality of brake chambers, two of which are shown at B2 and Such system also embodies an emergency line 66, a service'line 61 and a trailer reservoir 68, all of the foregoing being interconnected through a relay-emergency valve it of any suitable type, such as for example, that shown in the patent to S. Johnson, Jr., No. 2,018,212, granted October 22, 1935. The operation of the valve ii? is such that it normally connects the emergency line 65 with the reservoirBB to maintain the latter charged with air pressure from the tractor reservoir 16. The valve 16 is also of such construction as to connectthe trailer reservoir 68 with the brake chambers 62 and 66 through conduits i2 and M- whenever the service line 67 is charged with fluid pressure through operation of the tractor brake valve id. The construction is moreover also such, that in the event of a rupture of the emergency line 66, which would be caused for example by a break-in-two of the vehicles, the valve '50 would function automatically to supply air pressure to the brake chambers 62 and 64 from the reservoir 68 in order to eflect an emergency application of the trailer brakes.

From the foregoing, it will be readily appreciated that in order to effect a normal service application of the vehicle brakes, it is only necessary for the operator to depress the pedal of the tractor brake valve 40. This action serves to conduct air pressure from the reservoir 16 ,to the tractor brake chambers 22 by way of conduits 26, 27, 28, 30 and 32. Simultaneously, air pressure is conducted to the rear tractor brake chambers 24 by means of conduits 34, 3S and-38. In addition, the tractor service line 48 is charged with fluid pressure through conduits 50 and 52, in order to charge the trailer service line 67 to effect an application of the trailer brake chambers 62 and 64 through operation of the valve 18 which controls the trailer reservoir 68.

Should a severe leak occur in the service lines of the tractor or trailer, it will be readily understood that fluid pressure in the reservoirs M and i6 might be depleted so rapidly that an efficient application of the tractor and trailer brakes could not be eflected. Such a severe leak might be caused by a broken service line on the tractor or trailer or by reason of an accidental parting of the coupling 56. By the present invention, this difficulty is overcome and an efiicient application of the trailer brakes may be effected notwithstanding the occurrence of the aforesaid ruptured service lines.

In its broader aspect, the present invention includes an arrangement for positively interrupting the flow of air through the tractor service line 48 in the event that the rate of flow therethrough, due to'a broken'or ruptured service'line,

exceeds a predetermined value and persists for a predetermined time interval. More particularly, the arrangement comprises a fluid pressure responsive cut-ori valve it, positioned on the tractor and being arranged in series between conduits 5i] and 52. As shown, the valve 75 comprises a casing "is having inlet and outlet ports 89 and 82 which are respectively connected with the conduits 5i) and 52, flow of fluid pressure through said conduits being controlled by a normally open valve 8 3. A fluid pressure actuator 86 is positioned at the upper portion of th casing 13 and comprises a diaphragm 35 which is normally urged to the position shown by a spring 90, this action closing the valve B l through a diaphragm follower 82 which is provided with a rod 9 3 rigidly connected with the valve t l. The space above the diaphragm constitutes a control chamber 96 while the space beneath the diaphragm forms an atmospheric chamber 93, the latter being constantly open to the atmosphere through an opening H00. From this construction it will be clear that the normally open valve 8 3 may be closed in order to interrupt flow of air through the tractor service line 18, upon supplying the control chamber 96 with fluid pressure sufficient to overcome the tension of spring 98.

A novel arrangement is provided by the invention for controlling the application of fluid pressure to the cutoff valve 76 and more particularly, such arrangement is so constituted as to energize the valve and close off the service line in the event the latter is broken or develops serious leakage which might be sufficient to prevent efiicient application of any of the tractor brakes. More particularly, the foregoing construction includes a timing valve [62, a volume or timing reservoir HM and a fluid pressure actuated valve E06 which are eflective to supply fluid pressure to the control chamber 9% under conditions which will appear more fully hereinafter.

In order to obtain a measure of the flow conditions in the tractor service line as, the timing valve N32 is provided with a casing I933 having a fluid pressure actuator I it positioned at one'end thereof, the latter including a diaphragm 5H which forms, with the casing, a pair of opposite chambers H2 and H which are respectively connected to the tractor service line 48 at spacedapart points A and B through conduits H6 and H8, a duct H9 being provided in the casing 198 for connecting the conduit I I6 and the cham ber H2. Normally, the diaphragm iii is maintained in the position shown as by means of a spring 20 in order to connect the volume or timing reservoir 04 to the atmosphere by way of conduits E22 and lid, an outlet chamber Q26, an exhaust bore 128 formed in valve actuating member [36 carried by the diaphragm iii, and an exhaust chamber E32 which is in constant communication with an atmospheric connection I46 and also communicates with the bore 428 through ports 533, it being observed that the right hand end of the member we is spaced from an exhaust valve H34. However, it will be readily observed, that in the event the diaphragm Hi is moved to the right against the tension of the spring I20, such movement will first bring the be moved against the tension of a spring 436 in order to'open an inlet valve [38 and connect the. volume reservoir I04 with the service line conduit 50 by way of conduit IIE, passage I40 in the casing I08, inlet chamber I42, outlet chamber I26 and the interconnected conduits I24 and I22. Under these conditions, fluid under pressure will be conducted from the tractor brake valve to the volume reservoir to charge the latter. In order to regulate the rate of charging of the volume reservoir I04, a timing choke I44 may be incorporated in the passage Ida, and if desired, the atmospheric connection I46 associated with the exhaust chamber I32 may be restricted in order to maintain the cut-off valve 85 closed during operation of the brake valve 40 in its release position, as will appear more fully hereinafter.

In addition to the foregoing, the invention includes the fluid pressure actuated valve I05 which is connected with the volume reservoir, by way of conduits I48 and I22, and is connected with the control chamber 96 of the cut-off valve It by conduit I50. This valve is of the fluid pressure actuated type and may be constructed in a manner similar to the governor I8. During operation thereof, it is eiiective to connect the conduits I48 and I59 when a predetermined pressure is built up in the timing reservoir I54. On the other hand, when the volume reservoir pressure drops to a selected value, due to its being connected with the atmospheric connection I46 past the open exhaust valve I34, the valve I06 operates to out 01f communication between the conduits I48 and I59 and to connect the latter conduit to the atmosphere at the valve. Thus in the normal position of the parts illustrated, the control chamber 95 is vented to the atmosphere and the valve 84 will be in the open position to establish communication between the conduits 50 and 52 of the tractor service line 43.

In normal operation, application of the tractor brake valve 40 serves to charge the tractor brake chambers 22 and 24 and. to cause fluid pressure to flow through the tractor service line 43 so as to charge the trailer brake chambers 62 and 64 from the trailer reservoir 68 through operation of the relay-emergency valve It. During the initial charging of the tractor service line 48, the pressure differential acting across the diaphragm II I of the fiuid pressure actuator III created by the flow rate between the points of connection between the conduits IIE and IIS and the respective conduits 50 and 520i the tractor service line 48, see A and B, will move the said diaphragm to the right in order to disconnect the volume reservoir I54 from the atmospheric connection I 45 and establish a restricted communication between the reservoir and the conduit 50 of the tractor service line 48 by way of conduit I22, outlet chamber I26, inlet chamber I42, passage I40, timing choke I 44 and conduit H6. However, due to the volume of the reservoir I64 and to the flow capacity of the choke I44, the pressure built up in the said reservoir will be insufficient to actuate the fluid pressure actuated valve it during normal service applications. Thus as the pressure is built up in the trailer service line and the brake valve 40 is finally moved to a lapped position, the fluid pressure differential acting across the diaphragm III will decrease to the point where the spring I26 moves the member I39 to the position shown. This action enables the spring I36 to close the inlet valve I38 of the timing valve I02 and the volume reservoir I04 is reconnected with the atmospheric port I45 by way of the conduits I22 and I24, the

outlet chamber I26, bore I28 and the exhaust member I32. Thus during ordinary service brake applications, while the timing valve I02 operates to partially charge the volume reservoir, the cut-off valve will not function to interrupt the flow of fluid through the service lines of the vehicles. It will be understood, of course, that when the brake valve 40 is moved to exhaust position to release the vehicle brake chambers, the service lines 48 and 61 and the conduits H6 and I I8 will be vented to the atmosphere through the brake valve.

Assuming however that the service lines 48 and El are uncoupled at the coupling 56 or that the service line connection between the valves 86 and III is ruptured or develops a severe leak, then upon operation of the brake valve 40 to apply the brakes in service, the fluid actuator I III will operate in the same manner as aforesaid and the volume reservoir will again start to be charged with fluid under pressure. In this case, a substantially heavy flow of fluid for a much longer time will occur in the service line 48 and the timing valve I02 will be maintained in open position due to the continued application of the pressure differential across the diaphragm III and derived from the service line 48 at points A and B. Should such heavy flow continue for a sufficient length of time, the pressure built up in the volume reservoir I64 will finally be suflicient to operate the fluid pressure actuated valve I86 in order to interconnect the control chamber of the cut-off valve It with the tractor service conduit 50 as well as with the volume reservoir I94. When this occurs, the valve 34 will be positively moved to its closed position in order to interrupt further flow of fluid pressure through the tractor service line 48 and thus conserve such pressure to be utilized for effective braking of the brakes on the tractor.

From the construction provided, it will be readily understood that as soon as the tractor brake valve 46 is moved to its exhaust position, the conduit H8 will be exhausted and the return of the timing valve I62 to the position illustrated will exhaust the volume reservoir I84 as well as the conduit I48. Movement of the valve I05 to its normal position will exhaust the control chamber 96 and allow the spring 98 to open the valve 84. As heretofore pointed out, the exhaust connection I46 may be restricted if desired, in order to retard the exhausting of the reservoir I04. This action would maintain the cut-off valve It closed during a substantial portion of the brake valve release operation.

It is contemplated that in addition to the foregoing, the automatic closing of the cut-ofi valve IE will also occur during operaion of the brake valve 46 following a break-in-two of the vehicles. In such case, the loss of fluid pressure in the trailer emergency line 63 will cause an emergency application of the trailer brakes through operation of the relay-emergency valve III on the trailer. Although the tractor emergency line 42, will be vented to atmosphere under these conditions, the loss in pressure from the tractor reservoirs I4, II) will not be suilicient to prevent a full application of the tractor brakes. Thus during operation of the tractor brake valve 40 following a parting of the vehicles, the parts including the timing valve I02, the volume reservoir let, the pressure actuated valve IIIE and the cut-off valve I6 will function in the manner previously described in order to cut ofi the flow of fluid pressure through the tractor service line.

48. .Hence' even through pressure is being exhausted to atmosphere throughthe open tractor emergency line 42, still sufficient pressure will beavailable for effecting .an emergency. stop of the tractor.

From the foregoing, it will bereadily appreciated that the invention providesa novel and eflicient construction for conserving air .on the tractor in the event of a brokenserviceline or in the event that the vehicles areparted. The use of the cut-01f valve 76 insures that the loss of all the available fluid pressure on the tractor through the. tractor service iine will be positively prevented under the conditions outlined. It will also be appreciated that the. cooperationof thetiming valve I 52, the volumereservoir I65 and the pressure actuated valve I95. is such that the cut-oii valve 16 is not operated during ordinary service brake applications. These parts only function to close the tractor service line when the flow rate therethrough, caused by a leak or rupture, is sufficiently high and takes place for a suificient period of time as to allow the fluid pressure in the volume reservoir it;

tobuild up to the value suflicient to trip the valve 186. The flow rate through the tractor service line 48 is measured at the points A and B which may be respectively located adjacent th brake valve 4!] and adjacent the coupling 56. The only limitation as to the location of these points is that they shall be spaced apart a suiflcient distance as to cause the creation of a pressure differential which is high enough to move the diaphragm i H against the tension of the spring are.

While one embodiment of the invention has been disclosed and described herein with considerable particularity, it will be readily understood by those skilled in the art that various modifications may be resorted to without departing from the spirit of the invention. Reference will therefore be had to the appended claims for a definition of the limits of the invention.

What is claimed is:

1. In a fluid pressure operated vehicle braking system, a source of fluid pressure, a plurality of brake chambers, a brake valveccnnected with said source, a plurality of conduits connecting the brake valve and chambers, a normally open fluid pressure actuated valve in one of the conduits, and means to supply fluid pressure to the latter valve to close the same and interrupt the flow'of fluid pressure from the source to at least one .of the chambers, comprising a timing valve, and means for operating the timing valve in ac cordance with a predetermined pressure differential created between spaced-apart points in said one conduit due to the flow of fluid pressure therein.

2; In a fluid pressure operated vehicle braking system, a source of fiuid pressure, a plurality of brake chambers, a brake valve connected with said source, a plurality of conduits connecting the brake valve and chamber, a normally open fluidpressure actuated valve in one of the conduits, and means to supply fluid pressure to the latter valve to close the same and interrupt the flow of fluid pressure from the source to at least one of the chambers, comprising a timing valve, means for operating the timing valve in accordance with a predetermined pressure differential created between spaced-apart points in said one conduit due to the flow of fluid pressure therein, a connection between the timing valve and the fluid pressurezactuated'valve, and.

8 a fluidipressure responsive valve ior :controlling said :connection.

.3. vIn a fluid pressure operated vehicle braking system,ia source LOf fluid pressure, a plurality of brake chambers, a brake valve connected with said source, a plurality of conduits conmeeting the brake valve and chambers, a normally open fluid pressure actuated valvein one of the conduits, a timing valve, means for operating the timing valve in accordance with a predeterminedrpressure differential created between spaced-apart points in'said "one conduit due to the flow of 'fluidpressure'therein, and means effective after operation of said timing valve to establish a restricted communication be tween the brake valve and said fluidvpressure actuated valve.

4. In a fluid pressure operated vehicle braking system, a source of fluid pressure, .a plurality of brake chambers, a brake valve connected with said source, a plurality of conduitsconnecting the brake valve and chamber, atnormally open fluid pressure actuated valve in one of the conduits, a timing valve,'means for operating the timing valve in accordance with a predetermined pressure differential created between spaced-apart points in said one conduit due to the flow of fluid pressure therein, and means efiective after operation of said timing valve to establish a restricted communication between the brake valve and said fluid pressure actuated valve, said last named means including a fluid pressure responsive valve operable to establish said communication only after a predetermined rise in pressure therein.

5. In a fluid pressure operated vehicle braking system, a source of fluid pressure, a plurality of brake chambers, a brake valve connected with said source, a plurality of conduits connecting the brake valve and chamber, a normally open fluid pressure actuated valve in one of the conduits, and means to supply fluid pressure to the latter valve to close the same and interrupt the flow of fluid pressure from the source through said one conduit, comprising a connection between the brake valve and the fluid pressure actuated valve, a timing valve in said connection, means for operating the timing valve in accordance with a predetermined pressure differential created between spaced-apart points in said one conduit due to the flow 'oi fluid pressure therein, a volume reservoir communicating with said connection, and means operable only after the pressure in said volume reservoir has reached a predetermined value for opening that portion of the connection between'the timing valve and'the fluidpressure actuated valve.

6. A braking system as set forth in claim 5 which comprises in addition, a restriction in that portionor" the connection between the brake valve and the timing valve.

7. In a fluid pressure operated tractor-trailer braking system having interconnected tractor and trailer service and emergency lines, a source of fluid pressure on the tractor, a tractor brake valve for controlling the flow or" fluid pressure from said source through the service lines, and means for interrupting said flow of fluid pressure through the tractor service line when the flow therethrough reaches a predetermined rate, comprising a'normally open fluid pressure responsive valve in the tractor service line, a fluid pressure actuator movable in response to a predetermined pressure differential created between spaced-apart points in the tractor service line -due to the fluid pressure flow therethrough at said predetermined flow rate, and means including a timing valve operable by movement of said actuator for supplying fluid pressure to the fluid pressure responsive valve to close the same and thereby interrupt flow through the tractor service line.

8. In a fluid pressure operated tractor-trailer braking system having interconnected tractor and trailer service and emergency lines, a source of fluid pressure on the tractor, a tractor brake valve for controlling the flow of fluid pressure from said source through the service lines, a normally open fluid pressure responsive valve in the tractor service line, and means for supplying fluid pressure to said valve to close the same and interrupt flow of fluid through the tractor service line when said flow reaches a predetermined rate, comprising a connection extending from a point in the tractor service brake line between the brake valve and the fluid pressure responsive valve, to said latter valv a fluid pressure actuator movable in response to a predetermined pressure differential created between spaced-apart points in the tractor service line due to flow of fluid pressure therein, a timing valve normally closing said connection and movable to open position by movement of said actuator, and means including a fluid pressure actuated valve operable to establish communication through that portion of said connection between the timing valve and the fluid pressure responsive valve only after a predetermined rise in pressure in said portion.

9. in a fluid pressure operated tractor-trailer braking system having interconnected tractor and trailer service and emergency lines, a source of fluid pressure on the tractor, a tractor brake valve for controlling the flow o-f fluid pressure from said source through the service lines, a volume reservoir, a timing valve normally occupyin; a fir st position connecting the reservoir with the atmosphere and movable to a second position to interrupt the atmospheric [connection and connect the reservoir with the tractor brake system, means including a diaphragm for moving the timing valve to said second position, said diaphragm being subjected on opposite sides thereof to the respective pressures developed at spaced-apart points in the tractor service line, a normally open fluid pressure responsive valve in the tractor service line, and means actuated when the pressure of the fluid in said reservoir reaches a predetermined Value for connecting the reservoir with the fluid pressure responsive valve to close the latter.

10. In a fluid pressure operated tractor-trailer braking system having interconnected tractor and trailer service and emergency lines, a source of fluid pressure on the tractor, a tractor brake valve for controlling the flo-w of fluid pressure from said source through the service lines, a normally open fluid pressure responsive valve in the tractor service line, and means for supplying fluid pressure to said valve to close the same and interrupt flow of fluid through the tractor service line when said flow reaches a predetermined rate, comprising a connection extending from a point in the tractor service line between the brake valve and the fluid pressure responsive valve, to said latter valve, a fluid pressure actuator movable in response to a predetermined pressure differential created between spaced-apart points in the tractor service line due to flow of fluid pressure therein, a timing valve norm-ally closing said connection and movable to open position by movement of said actuator, and means for controlling the flow of fluid pressure in that portion of said connection between the timing valve and the fluid pressure responsive valve, comprising a volume reservoir for storing fluid flowing to said portion past the open timing valve, and a fluid pressure actuated valve operable to open said portion of the connection when the pressure of the fluid in the volume reservoir reaches. a predetermined value.

11. In a fluid pressure operated tractor-trailer braking system having interconnected tractor and trailer service and emergency lines, a source of fluid pressure on the tractor, a tractor brake valve for controlling the flow of fluid pressure from said source through the service lines, a normally open fluid pressure responsive valve in the tractor service line, a volume reservoir, means responsive to a predetermined pressure differential created between spaced-apart points in the tractor service line for establishing a restricted communication between the volume reservoir and the tractor service line, and means responsive to a predetermined pressure built up in the volume reservoir to connect the reservoir and the fluid pressure responsive valve to move the latter to closed position and thereby through the tractor service line.

12. In a fluid pressure operated tractor-trailer braking system having interconnected tractor and trailer service and emergency lines, a source of fluid pressure on the tractor, a tractor brake valve for controlling the flow of fluid pressure from said source through the service lines, a normally open fluid pressure responsive valve in the tractor service line, a volume reservoir, a timing valve normally occupying one position to connect the volume reservoir to atmosphere and movable to another position to connect said reservoir with the tractor service line, a fluid pressure actuator responsive to a predetermined pressure differential created between spaced-apart points in the tractor service line for moving said timing valve from said one position to said another position, and a fluid pressure operated valve movable to connect said reservoir and the fluid pressure responsive valve to close the latter when the pressure in said reservoir reaches a predetermined value.

13. In a fluid pressure operated tractor-trailer braking system having interconnected tractor and trailer service and emergency lines, a source of fluid pressure on the tractor, a tractor brake valve for controlling the flow of fluid pressure from said source through the service lines, a volume reservoir, means responsive to a predetermined pressure diiT-erential created between spaced-apart points in the tractor service line for establishing communication between the volume reservoir and the tractor service line, a normally open valve in the tractor service line and normally efiective to allow fluid flow between said points, and means operable when a predetermined pressure has been built up in said reservoir to close said normally open valve.

14. In .a fluid pressure operated vehicle braking system, a source of fluid pressure, a plurality of brake chambers, a brake valve connected with said source, a plurality of conduits connecting the brake valve and chambers, a normally open valve in one of said conduits, a fluid pressure actuator for said latter valve, and means to supply fluid pressure to said actuator to close the normally open valve and interrupt the flow of interrupt flow 11 fluid; pressure from the source through said. one conduit, comprising a connection withisaid one conduit between the brake valve and the normally open valve and extending to said actuator, a normally closed timing valve in said connection, a fluid pressure responsive element movable to open said timing valve, means to subject one side of said element to the fluid pressure in said connection, and means to subject the other side of said element to the fluid pressure existing in said one 10 Number conduit between the normally open valve and one of the chambers.

15. A system as set forth in claim 14 which comprises in addition, a fluid pressure responsive valve in said connection operable to establish 15 3 12 fluid. flow to saidactuator only after arpredetermined rise in fluid pressure insaidiconnection.

ELLERY R. FITCH.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date 1,956,691 McCune May 1, 1934 1,969,812 MoCune Aug. 14, 1934 2,084,707 Robinson June 22, 1937 2,248,437 Robinson July 8, 1941 Williams et al Oct. 12, 1948 

